1. Field of the Invention
The present invention relates to a charge control agent for electrophotography etc., and a toner for developing electrostatic latent images using said charge control agent.
2. Description of the Prior Art
In copying machines and other instruments based on electrophotography, various toners containing a coloring agent, a fixing resin and other substances are used to visualize the electrostatic latent image formed on the photoreceptor having a photosensitive layer containing a photoconductive substance. Such toners are required to show satisfactory performance in terms of chargeability, fixability, offset resistance, durability, etc.
In recent years, to achieve image quality improvement, while copying and printing speeds are increased, there have been increased demands for improved charge characteristics of toners, such as increased charge rise speeds, and for toner fixability on recording papers, such as excellent low-temperature fixability and offset resistance. Such demands for improved toner performance are intensifying with the advance in performance sophistication of copying machines and printers.
Chargeability is a key factor in electrostatic latent image-developing systems. Thus, to appropriately control the chargeability of a toner, a charge control agent providing a positive or negative charge is often added to the toner. Of the conventional charge control agents in actual application, those providing a positive charge for a toner include nigrosine dyes and quaternary ammonium salt compounds. Guanidine, imidazole derivatives, etc. have also been proposed as such toners. Those providing a negative charge for a toner include salicylic acid derivative metal compounds and azo dye-metal complexes.
Many of the conventional charge control agents which are salicylic acid derivative metal compounds, azo dye-metal complexes or quaternary ammonium salts provide excellent chargeability when added to a toner. However, some problems remain to be resolved, including poor fluidity of the charge control agent itself, unsatisfactory levels of dispersibility in fixing resins and durability in multiple repeated use of toners, and relatively low clearness of initial copying images due to insufficient charge rise speeds.
The present invention was developed in view of the above problems in the prior art, and is directed to provide a charge control agent which is excellent in charge control substance uniform dispersibility in resins for toners, sharp and highly uniform in charge amount distribution, quick in charge rise, and excellent in charge stability over time, non-dependency on environment, storage stability and durability, and which does not adversely affect toner fixability and offset resistance when used in toners of various compositions; a manufacturing process thereof; and a toner for developing electrostatic images containing said charge control agent.